A communication system supports a multi-carrier for extending transmission capacity.
In the multi-carrier, a non-arrangement phenomenon of a protocol data unit (PDU) that does not occur in a single-carrier may occur. The PDU should be re-arranged in order to solve the non-arrangement phenomenon. However, in order to re-arrange the PDU, a sequence number (SN) should be inserted into all the PDUs, thereby wasting wireless resources.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.